Transmission line quality, including voltage and Volt-Ampere Reactive (VAR) fluctuations can be greatly affected by the type and function of the wind power generation system employed. Excess reactive power in electrical system's can cause excessive heating in the components causing premature failure. In addition, uncontrolled reactive power leads to voltage fluctuations that exceed the equipment specifications causing component failure. Finally, uncontrolled reactive power can lead to extreme inefficiencies with respect to power transmission, thus increasing the cost to transfer power across the grid.
Operators of transmission and distribution systems, electrical generating plants, and factories have known about this issue for quite some time. To compensate for voltage and VAR fluctuations, operators and utilities install equipment to compensate the reactive nature of their systems. Traditionally, both capacitors and reactors are used for this compensation. Capacitor banks retain or produce reactive power, measured in VARs, and reactor banks consume VARs. Depending on the VARs measured on the system, the operator would enable one of these devices. The capacitors and reactors purpose is either to minimize the total amount of VARs flowing or to achieve a desired running voltage. Currently, the manufactures of these devices provide them with microprocessor based controllers so that they can be automatically cycled.
Usually, wind plants are located at the end of radial feeder. Usually, without some form of voltage control, the voltage at the wind farm could go out of operating specifications. This issue is generally handled by load flow studies performed before construction begins so as to assess the performance of the transmission system. To compensate for excessive voltage swings utilities install equipment on their electrical networks to control the amount of VARs that flow, usually in the form of capacitors or reactor banks.
A controller may be installed that runs a program that monitors the changing grid conditions, and either connects or disconnects the capacitor/reactor bank to or from the grid. The controller collects data from sensors sensing the various grid conditions. The controller compares the sensor readings to the pre-programmed commands, and responds to them. However, the current design of these devices does not allow them to quickly respond to changing grid conditions. In addition, these devices are not adjustable. For example, capacitor banks need to discharge when disconnected from the transmission system and cannot reconnect for five minutes. Furthermore, capacitor and reactor banks change the VAR flow by a set amount, which can result in over or under compensation. Some manufactures have tried to resolve this problem by making fast adjustable reactive power devices. However, utility companies may be reluctant to install such devices due to their great expense.
In many wind turbine sites, the utility company finds it necessary to curtail or slow production because of grid problems inherent with the grid or the wind farm.
In some cases, if the utility company wants to change the setting in a wind park control unit, the utility company has to call the wind farm site Operations and Maintenance (O&M) personnel and have them drive to the substation to facilitate the change. Depending on the lay out of the wind farm site, this can take up to an hour or more to reach the appropriate substation.